Discharge tube



I Julie 1930- J. H. DE'BOER ET AL 1,767,437

I I mscxmzaa wuss Filed Oct. 18, 1926 Patented June 24, 1930 UNIEDSTATES.

PATENT. OFFICE JAN HENDRIK DE BOER AND PIETER CLAUSING, OF EINDH OVEN,NETHERLANDS, AS- SIGNORS TO N. V. PHILIPS GLOEILAMPENFABRIEKEN, OFEINDI-IOVEN, NETHER- LANDS DISCHARGE TUBE Application filed October 18,1926, Serial No. 142,498, and in the Netherlands December 12,1925.

This invention has reference to a process of introducing potassium orcaesium or rubidium intoan electric discharge tube. The

introduction of these metals as such into an electric discharge tube isbeset with difliculties as the metals are quite readily oxidized in airso that it is diflicult to introduce them in a pure state intothedischarge tube.

The object of the invention is to provide for a process that obviatesthis difficulty and by which it has been found possible to introducepotassium, caesium and rubidium in an entirely pure state into adischarge tube.

According to the invention the process of introducing potassium orcaesium or rubidium into an electric discharge tube consists inintroducing a mixture of one or more p0- tassium or cmsium or rubidiumcompounds with one or more of the azides of the metals of the secondprincipal group of the periodic system into the discharge tube or into areceptacle united to the discharge tube, after which metallic potassiumor cmsium or rue bidium is formed from the said mixture by the presenceof heat.

Preferably barium azide (BaN should be used as the azide of the metalsof the second principal group ofthe periodic system. The mixture of thepotassium or caesium or rubidium compounds with an azide may beintroduced into the discharge tube or into the receptacle united to it,in a solid state or in the form of a solution. After volatilization ofany solvent that may be present, the mixture is gently heated, by reasonof which the azide is decomposed and the metal of the second principalgroup of-the periodic system thus liberated reduces the potassium orcaesium or rubidium salt into metallic potassium or caesium or rubidium.As these metals are very volatile, even when gently heated, thedischarge tube will be filled With potassium or caesium or rubidiumvapour of very low pressure.

It is not necessary that the mixture of potassium or caesium or rubidiumsalts and acids should be arranged in a side tubule of the dischargetube; it may be arranged at other points of the discharge tube if onlyNow, according to Langmuirs researches,

such an incandescent cathode may be heated to a temperature that exceedsby many hundreds of degrees the melting point of potassium or caesium orrubidium Without the latter volatilizing noticeably and will thus yieldan electron emission which in consequence of the extremely lowRichardsons constant of potassium, caesium and rubidium is very high.

Potassium or caesium or rubidium introduced by the process according tothe invention, into an incandescent cathode discharge tube or into adischarge tube comprising a cold cathode may combine With any gasresidues that have remained in the discharge tube in spite of the latterbeing exhausted as far as possible, the prejudicial effect of such gasesbeing thus neutralized.

The invention will be clearly understood by reference to theaccompanying drawing in Which 1 is a bulb of the discharge tube in whichan incandescent cathode 2 consisting of tungsten, a grid 3 and an anode4 are concentrically arranged. The bulb of the discharge tube has sealedto it a side tubule 5 with a receptacle 6 into which a mixture ofcaesium chloride and barium azide in aqueous solution has beenintroduced before hand. The discharge tube is then exhausted until thesolvent has left the receptacle 6 by volatilization and the mixture ofcaesium chloride and barium azide remains in a solid state. After thedischarge tube has been sealed off the pump, the receptacle 6 is gentlyheated, the barium azide being thus decomposed. By reason of the heatingtemperature being slightly increased the caesium chloride is reduced bythe liberated barium into metallic caesium which spreads throughout theinterior of the discharge tube. The side tubule 5 With the receptacle 6may then be sealed oii the discharge tube.

The metals potassium and rubidium may be similarly introduced. into anelectric discharge tube.

hat I claim is l. The process Which comprises introducing into adischarge tube a mixture of an alkali-metal compound With the azide of ametal of the second principal group of the periodic system, andsubsequently liberating the alkali-metal from the said mixture by thepresence of heat.

2. The process of introducing an alkalimetal vapor into a discharge tubewhich comprises first introducing into a receptacle connected to adischarge tube a mixture of an alkali-metal compound with the azide of ametal of the second principal group of the periodic system andsubsequently liberating the alkali-metal from the said mixture by thepresence of heat.

In testimony whereof we aifix our signatures, at the city of Eindhoven,this 1st of October 1926.

JAN HENDRIK DE BOER. PIETER CLAUSING.

